US4375090A — Method for interpreting seismic records to yield …

Claim 1

Independent Claim 255 words

System for resolving event characteristics of a seismic record so as to determine gas/oil fractions in a selected zone of an earth formation by creating synthetic gas/oil-indicating characteristics from brine-saturated petrophysical parameters corresponding to each selected zone of interest, and comparing such characteristics with said record comprising: (A) Means for obtaining said seismic record for at least said selected zone; (B) Means for determining actual compressional velocity and density values of said zone of interest based on field information associated with a known zonal lithology selected from a group comprising sandstone, limestone and dolostone; (C) A programmable digital computer for: (i) from the parameters of (B), generating a brine-saturated P-wave modulus value corresponding to said zone of interest; (ii) from said generated brine-saturated P-wave modulus value of (i), predicting compressional velocities of said zone with gas/oil in differing amounts present in said zone, in accordance with the relationship ##EQU12## where rho-b is the bulk density, φ is the porosity, G* is the shear modulus at the saturations of interest, Kf equals the bulk modulus for the liquid-gas mixture, Ka is the frame modulus, Km is the bulk modulus of a hypothetical rock, i.e., same composition but perfectly cemented with zero porosity; (iii) from seismic velocities of (B), predicting synthetic seismic amplitude information with gas/oil present in said zone in differing amounts; and (iv) comparing said predicted amplitude information with actual field-acquired amplitude data associated with said seismic record of (A) so as to determine both presence and amounts of gas/oil within said zone of interest.

Claim 2

Dependent Claim 255 words

System for resolving event characteristics of a seismic record so as to determine gas/oil fractions in a selected zone of an earth formation by creating synthetic gas/oil-indicating characteristics from brine-saturated petrophysical parameters corresponding to each selected zone of interest, and comparing such characteristics with said record comprising: (A) Means for obtaining said seismic record for at least said selected zone; (B) Means for determining actual compressional velocity and density values of said zone of interest based on field information associated with a known zonal lithology selected from a group comprising sandstone, limestone and dolostone; (C) A programmable digital computer for: (i) from the parameters of (B), generating a brine-saturated P-wave modulus value corresponding to said zone of interest; (ii) from said generated brine-saturated P-wave modulus value of (i), predicting compressional velocities of said zone with gas/oil in differing amounts present in said zone, in accordance with the relationship ##EQU12## where rho-b is the bulk density, φ is the porosity, G* is the shear modulus at the saturations of interest, Kf equals the bulk modulus for the liquid-gas mixture, Ka is the frame modulus, Km is the bulk modulus of a hypothetical rock, i.e., same composition but perfectly cemented with zero porosity; (iii) from seismic velocities of (B), predicting synthetic seismic amplitude information with gas/oil present in said zone in differing amounts; and (iv) comparing said predicted amplitude information with actual field-acquired amplitude data associated with said seismic record of (A) so as to determine both presence and amounts of gas/oil within said zone of interest.

Claim 3

Dependent Claim 141 words

System of claim 1 in which (ii) is further characterized by: simultaneously solving through iteration the following equations: ##EQU13## to provide estimations of Ka and G* as a function of fluid saturation, where: rho-b is the bulk density of the zone of interest, Vp is the compressional velocity, P* is the P-wave modulus at said saturations of interest, K* is the bulk modulus at said saturations of interest, G* is the shear modulus at said saturations of interest, Ka and Ga are frame moduli, Kfc is the fluid correction equal to K*-Ka, Km and Gm are the bulk and shear moduli of a hypothetical rock (i.e., same composition but perfectly cemented with zero porosity), φ=porosity a=Ka/Km b=K*/Km g=G*/Gm=Ga/Gm f=(Km/Kf)-1 C is an empirical parameter and f 3 describes a functional operator which relates to the variables of interest of Equation (3).

Claim 4

Dependent Claim 150 words

System of claim 2 in which said iteration involves: (i)' predicting brine-saturated bulk and shear moduli (Kw* and Gw*) using empirical equations containing coefficients and a P-wave modulus value (Pw*), said coefficients varying in empirical fashion as a function of at least porosity, pressure and temperature, said P-wave modulus value (Pw*) being a P-wave modulus value for a brine-saturated rock which corresponds to said zone of interest based on well logging geologic data, said shear modulus value Gw* being equal to Ggas/oil* where Ggas/oil* is the shear modulus of said zone with gas/oil present; (ii)' estimating frame modulus values (Ka) of said zone of interest using a relationship involving Kw*, Kb, Km and φ, where Kw* is brine-saturated bulk density of the aggregate, Kb is the bulk modulus of brine, and Km is the bulk modulus of the solid material making up the zone of interest and φ is porosity.

Claim 5

Dependent Claim 239 words

Method for resolving event characteristics of a seismic record so as to determine gas/oil fractions in a selected zone of an earth formation by creating synthetic gas/oil-indicating characteristics from brine-saturated petrophysical parameters corresponding to each selected zone of interest, and comparing such characteristics with said record comprising the steps of: (a) obtaining said seismic record for at least said selected zone by field measurement; (b) determining actual compressional velocity and density values of said zone of interest based on field information associated with a known zonal lithology selected from a group comprising sandstone, limestone and dolostone; (c) from the parameters of (b), generating a brine-saturated P-wave modulus value corresponding to said zone of interest; (d) from said brine-saturated P-wave modulus value of (c), predicting P-wave moduli of said zone with gas/oil in differing amounts present in said zone, in accordance with the relationship ##EQU14## where Pgas/oil* is the predicted P-wave modulus with gas/oil present in predetermined amounts; Kgas/oil* is the predicted bulk modulus of said zone with gas/oil present in said predetermined amounts; GW* is the brine-saturated shear modulus of said zone; (e) from seismic velocities of said zone calculated from step (d), predicting synthetic seismic values associated with different gas/oil fractions present in said zone; and (f) comparing said synthetic seismic values with actual field-acquired values associated with said seismic record of (a) so as to determine both presence and amounts of gas/oil within said zone of interest.

Claim 6

Dependent Claim 239 words

Method for resolving event characteristics of a seismic record so as to determine gas/oil fractions in a selected zone of an earth formation by creating synthetic gas/oil-indicating characteristics from brine-saturated petrophysical parameters corresponding to each selected zone of interest, and comparing such characteristics with said record comprising the steps of: (a) obtaining said seismic record for at least said selected zone by field measurement; (b) determining actual compressional velocity and density values of said zone of interest based on field information associated with a known zonal lithology selected from a group comprising sandstone, limestone and dolostone; (c) from the parameters of (b), generating a brine-saturated P-wave modulus value corresponding to said zone of interest; (d) from said brine-saturated P-wave modulus value of (c), predicting P-wave moduli of said zone with gas/oil in differing amounts present in said zone, in accordance with the relationship ##EQU14## where Pgas/oil* is the predicted P-wave modulus with gas/oil present in predetermined amounts; Kgas/oil* is the predicted bulk modulus of said zone with gas/oil present in said predetermined amounts; GW* is the brine-saturated shear modulus of said zone; (e) from seismic velocities of said zone calculated from step (d), predicting synthetic seismic values associated with different gas/oil fractions present in said zone; and (f) comparing said synthetic seismic values with actual field-acquired values associated with said seismic record of (a) so as to determine both presence and amounts of gas/oil within said zone of interest.

Claim 7

Dependent Claim 92 words

Method of claim 4 in which said synthetic seismic values are estimated amplitude values determined in accordance with ##EQU15## where Ar is the amplitude from the reflected signal at said zone of interest and Ai is the amplitude of the incident signal; V 1 is the compressional velocity of the wave in an overlying medium 1; V 2 is the compressional velocity in the zone of interest below the contact line; d 1 is the density of the overlying medium 1; and d 2 is the density of the underlying medium 2.

Claim 8

Dependent Claim 245 words

Method for resolving event characteristics of a seismic record so as to determine gas/oil fractions in a selected zone of an earth formation by creating synthetic gas/oil-indicating characteristics from brine-saturated petrophysical parameters corresponding to each selected zone of interest, and comparing such characteristics with said record comprising the steps of: (a) obtaining said seismic record for at least said selected zone by field measurement; (b) determining actual compressional velocity and density values of said zone of interest based on field information associated with a known zonal lithology selected from a group comprising sandstone, limestone and dolostone; (c) from brine-saturated P-wave modulus values corresponding to said zone of interest generated using the values of (b), predicting velocities of said zone as a function of gas/oil in differing amounts in said zone, in accordance with the relationship ##EQU16## where rho-b is the bulk density, φ is the porosity, G* is the shear modulus at the saturations of interest, Ka is the frame modulus, Kf equals the bulk modulus for the liquid-gas mixture, Km is the bulk modulus of a hypothetical rock, i.e., same composition but perfectly cemented with zero porosity; (d) from velocities of said zone calculated from step (c), predicting synthetic amplitude information with gas/oil present in said zone; and (e) comparing said predicted amplitude information with gas/oil present with actual field-acquired amplitude data associated with said seismic record of (a) so as to determine both presence and amounts of gas/oil within said zone of interest.

Claim 9

Dependent Claim 245 words

Method for resolving event characteristics of a seismic record so as to determine gas/oil fractions in a selected zone of an earth formation by creating synthetic gas/oil-indicating characteristics from brine-saturated petrophysical parameters corresponding to each selected zone of interest, and comparing such characteristics with said record comprising the steps of: (a) obtaining said seismic record for at least said selected zone by field measurement; (b) determining actual compressional velocity and density values of said zone of interest based on field information associated with a known zonal lithology selected from a group comprising sandstone, limestone and dolostone; (c) from brine-saturated P-wave modulus values corresponding to said zone of interest generated using the values of (b), predicting velocities of said zone as a function of gas/oil in differing amounts in said zone, in accordance with the relationship ##EQU16## where rho-b is the bulk density, φ is the porosity, G* is the shear modulus at the saturations of interest, Ka is the frame modulus, Kf equals the bulk modulus for the liquid-gas mixture, Km is the bulk modulus of a hypothetical rock, i.e., same composition but perfectly cemented with zero porosity; (d) from velocities of said zone calculated from step (c), predicting synthetic amplitude information with gas/oil present in said zone; and (e) comparing said predicted amplitude information with gas/oil present with actual field-acquired amplitude data associated with said seismic record of (a) so as to determine both presence and amounts of gas/oil within said zone of interest.

Claim 10

Dependent Claim 140 words

Method of claim 6 in which step (c) is further characterized by: simultaneously solving through iteration the following equations: ##EQU17## to provide estimations of Ka and G* as a function of fluid saturation, where: rho-b is the bulk density of the zone of interest, Vp is the compressional velocity, P* is the P-wave modulus at said saturations of interest, K* is the bulk modulus at said saturations of interest, G* is the shear modulus at said saturations of interest, Ka and Ga are the frame moduli, Kfc is the fluid correction equal to K*-Ka, Km and Gm are the bulk and shear moduli of a hypothetical rock (i.e., same composition but perfectly cemented with zero porosity), φ=porosity a=Ka/Km b=K*/Km g=G*/Gm=Ga/Gm f=(Km/Kf)-1 C is an empirical parameter, and f 3 describes a functional operation which relates the variables of Equation (3).

Claim 11

Dependent Claim 35 words

Method of claim 7 in which said K* of said iteration comprising a gas modulus component (Kg*) and oil bulk modulus (Koil*) at selected saturations and gravities, and whose saturations vary in accordance with Soil+Sgas<1.0.

Claim 12

Dependent Claim 97 words

Method of claim 8 in which said gas bulk modulus component (Kg*) is calculated under the isothermal form of Benedict-Webb-Rubin in accordance with the equation ##EQU18## where: (i) Kg*pr is the pseudo-reduced bulk modulus equal to the first term of the above equation in which X is the reciprocal of the pseudo-reduced volume, Tpr is the pseudo temperature, Cr and gamma-r are coefficients and S 1 and S 2 are functions of Tr and S 3 is a function of gamma-r; and (ii) Ppc is the pseudo-critical pressure which varies as a function of gas gravity (gamma).

Claim 13

Dependent Claim 33 words

Method of claim 8 in which said oil bulk modulus Koil* is calculated in accordance with the equation Koil*=36 Poil-19.6=141.5/gamma-oil+131.5 where Poil is the oil density and gamma-oil is the oil gravity (API).

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1986-02-21	1986-08-23	1987-02-22	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1990-02-21	1990-08-23	1991-02-22	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	1994-02-21	1994-08-23	1995-02-22	$7700.00	Window Closed / Lapsed

Method for interpreting seismic records to yield indications of gas/oil in an earth formation such as a sandstone, limestone, or dolostone

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